Jefferson Lab Experiment E91-016

This setting was chosen such as to minimze the recoil momentum to the produced lambda or hypernucleus. Base on the assumption that
the sticking probability of the hyperon to the residual nucleus falls off steeply with increasing recoil momentum this setting should give the highest yield for bound hypernuclei. It also leads to the largest separation of the quasifree distributions for lambda and sigma production.

The upper left graph shows with the blue curve the relation between electron and virtual photon angle for a fixed Q² of 0.348 GeV². The vertical black line is the minimum HMS angle of 10.5 degree, the horizontal line the minimum SOS angle of 13.30 degree and the diagonal line the minimum separation angle between the two spectrometers of 28.30 degree. The other three graphs show the corresponding range in W, kaon momentum, and recoil momentum. Here the blue lines represent the kinematics on a hydrogen target, p(e,e'K⁺)lambda, and the red lines the kinematics for lambda production at the threshold for D₂ and ³He and ⁴He targets. The black dots indicate the E91-016 kinematics. In principle a lower value for Q2 would be accessible. The blue line in the upper left graph would move further to the left. However, the restriction imposed by the minimum opening angle would then require a larger virtual photon angle, which results in a higher recoil momentum. Thus the chosen setting is considered to be the optimal choice with respect to the transfered momentum. Further, the resulting kaon momentum is in a range which, both, gives a still reasonable survival probability and also allows for good particle identification by means of time-of-flight.